1. Field of the Invention
The present invention relates to a shielding device, and more particularly to an electro magnetic (EM) wave shielding device, which covers a test point region of a circuit board.
2. Related Art
With the rapid progress of the electronic science, functions and applications of various electronic products become increasingly diversified, and accordingly, the design and development of the printed circuit boards (PCBs) disposed in the electronic products face greater challenge. During the manufacturing of the circuit boards, in order to exclude non-researching and non-designing faults, for example, short circuit or disconnecting problems resulted from a poor manufacturing process of the circuit boards, or problems (for example, mis-insertion of parts) resulted from carelessness during the assembling process on the production line, in-circuit test (ICT) including short circuit or disconnecting test must be performed before a large shipment of circuit boards, so as to ensure the shipment quality of the circuit boards.
Currently, as for a method for confirming the quality of the circuit board, specific wires for testing electrical functions are usually configured among a plurality of wires printed on a surface of the circuit board. Meanwhile, test points electrically connected to the wires are disposed on the circuit board. Then, testing jigs for testing the test points are provided, so as to perform the ICT testing operation on the quality of the circuit board. However, once the quality test of the circuit board is finished, the test points disposed on the circuit board do not have any other function, but become one of the sources for producing EM interferences (EMIs) of the PCB.
The EMI has become one of the severe problems in the current electronic industry, which causes interferences to other electronic elements disposed on the circuit board, and influences the normal running operations thereof, such that the EMI must be reduced as much as possible. Recently, considering the method for lowering the EMI, in addition to disposing a ground layer on the circuit board, a ground copper foil is usually laid on a test point region, so as to increase a grounding area, thereby lowering the EMI by reducing the impedance of certain grounding loops. Alternatively, a metal shield mask is disposed on the test point region, thereby lowering the EMI. However, the EM wave shielding capability of the copper foil is rather limited, and thus, no desirable EMI shielding effects can be provided. Although the EM wave shielding capability of the metal shield mask is better than that of the copper foil, the metal shield mask occupies a certain volume in usage, and a space on the circuit board for disposing the metal shield mask is quite limited, such that the usage of the metal shield mask is restricted to a large extent.
Therefore, as for the EMI problem of the test point region on the circuit board, people in the industry are still searching for an EMI shielding method capable of overcoming the usage restrictions due to the limited space of the circuit board and improving the shielding capability.